The invention relates generally to pattern analysis and more particularly to two dimensional pattern analysis performed by attenuating and isolating spatial frequency subsets of a transform of the pattern. Transform attenuation corresponding to the variations of human contrast sensitivity over 360.degree. orientation may be used to bias two dimensional transform data such that one, two and three dimensional pattern information in spatial frequency subsets may be extracted by using conventional bandpass spatial filters. In addition, the conventional bandpass spatial filter may provide depth information by uniquely using it in combination with the transform with or without the transform attenuation corresponding to variations of human contrast sensitivity.
The prior art has attempted similar two dimensional pattern analysis using contrast sensitivity data; however, any contrast sensitivity attenuation attempted was performed isotropically over 360.degree.. Also, special binary valued, wedge-type filters were used to obtain spatial frequency information at various orientations. However, these devices required complex means for extracting the pattern elements to create special frequency signature rather than enabling the ulitization of simple thresholding to obtain the same result for many tasks. Basic pattern information previously required heuristic low pass bandpass spatial filters. None of the prior art devices were able to obtain large amounts of relevant pattern information from two dimensional spatial frequency information because the attenuation characteristics for orientation and spatial frequency and relevant spatial frequency bands were not recognized or determined. Furthermore, third dimensional depth information in terms of spatial frequency subsets and reconstructed intensity gradients has been beyond the realm of the two dimensional pattern analysis systems heretofore contemplated. Finally, two dimensional pattern analysis previously developed does not have the unification or parsimony of the methods outlined herein.